Reception antenna for optical image formation device using nuclear magnetic resonance

Abstract

In the invention, the quality of the signal received is improved by symmetrizing the antenna. To this end, this antenna comprises two cords each of which has a symmetry with respect to one and the same plane (XOZ). These cords are linked by their ends to antenna tuning capacitors. The received signal is taken up by a high-frequency line integrated to one of the cords at the connection point of one of the tuning capacitors. Furthermore, the other end of this high-frequency line, arranged in the plane of symmetry, is linked to an impedance amplifier-transformer circuit with a high input impedance.

What is claimed is: 
     
       1. A reception antenna for an optical image formation device using nuclear magnetic resonance by which a body is subjected to a constant magnetic field and to a radio-frequency excitation from an emitting antenna causing a resonance of the oscillation of the magnetic moments of the particles of said body and wherein as soon as said radio-frequency excitation ceases, a measurement is made of the resonant signal emitted by said body when the magnetic moments of the particles tend to become realigned with said constant magnetic field, said reception antenna including a means for symmetrization in order to receive said resonance signal and to provide for the transformation of the impedance of said reception antenna in order to transmit said resonance signal wherein said means for symmetrization and transformation comprises: a conductive loop which is frequency tuned by at least one capacitor means arranged symmetrically in said conductive loop;   a reception circuit for receiving a signal induced in said conductive loop wherein said reception circuit provides for said impedance transformation and wherein said reception circuit is connected to the terminals of one of said at least one capacitor means and wherein said conductive loop includes a first section comprising a portion of a high frequency line and a second section in series connection to said first section;   wherein said portion of said high frequency line has a ground conductor which is a part of said conductive loop and a core conductor which is connected in order to conduct said resonance signal wherein said core conductor is connected to a terminal of said second section of said loop and to said reception circuit providing said impedance transformation.   
     
     
       2. Antenna according to the claim 1 wherein the loop exhibits a geometrical symmetry with respect to a plane substantially transverse to the plane of said loop. 
     
     
       3. Antenna according to claim 2 wherein the end of the high-frequency line section connected to the impedance transformation circuit is contained in the plane of symmetry. 
     
     
       4. Antenna according to any one of the claims 1, 2, 3 wherein the section of the conductor which forms said second section is that of a coaxial cable identical to that of the high-frequency line section 
     
     
       5. Antenna according to any one of the claims 1, 2, 3 wherein the impedance transformation circuit is a high input impedance circuit. 
     
     
       6. Antenna according to claim 5 wherein the impedance transformation circuit is placed in the immediate vicinity of the antenna. 
     
     
       7. Antenna according to claim 6 wherein the impedance transformation circuit comprises a field effect transistor mounted as a common emitter. 
     
     
       8. Antenna according to the claim 7 wherein the field effect transistor is powered by a polarizing voltage decoupled power source. 
     
     
       9. Antenna according to the claim 3 wherein said at least one capacitor means includes tuning capacitances of two symmetrical parts of the loop wherein said tuning capacitances are equal.